1. Field of the Invention
In this specification, the term "convex surface" refers to a surface in which a center portion of an element of glass material is swollen or enlarged as compared to the periphery of the element of glass material. The term "concave surface" refers to a surface in which a center portion of an element of glass material is caved in or reduced in thickness as compared to the periphery of the element of glass material. Finally, the term "element group" refers to a group of refractive surfaces; such a group is not always surrounded by mediums such as air.
This invention relates to a projection optical system used in a projection exposure apparatus which transcribes a reticle having an electric circuit pattern onto a surface of a semiconductor wafer.
2. Description of Related Art
Conventionally, in production of IC and LSI integrated circuits and liquid crystal flat displays, projection exposure methods using projection exposure apparatuses are used.
In these kinds of projection exposure apparatuses, in order to provide excellent resolution and an exposure area of sufficient width, projection optical systems such as those disclosed in U.S. Pat. No. 5,260,832 and Laid-Open Japanese Patent Publication 7-140384 are used.
The integrated circuit patterns of semiconductors are becoming increasingly microscopic. The necessary exposure areas of the liquid crystal flat displays, moreover, are becoming wider.
In this context, the optical performance required for a projection optical system used for IC exposure needs to be further improved. Conventional high performance Gaussian types of systems, such as that forming the subject matter of U.S. Pat. No. 5,260,832, are becoming inadequate.
A five-group construction projection optical system is disclosed in Japanese Laid-Open Patent Publication 7-140384. In this case, among three positive refractive power convex lens groups, one pair of convex lenses opposing each other has weak refraction power. This pair cannot sufficiently converge a light flux or bundle generated in a concave lens group having negative refractive power. Thus, it is difficult to achieve a sufficiently small overall optical system.